DSpace community: 航空太空工程學系暨研究所
https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/83
本系創設於民國六十一年,是國內民間大學中成立最早之航空工程系,歷屆系友已有二千餘人,七十七學年度起奉准每年招收雙班學生一百二十人,八十五學年度起由航空工程改名為航空太空工程學系並同時成立研究所。The community's search engineSearch the Channels
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Bulge formation of liquid film at the trailing edge: Scaling laws and particle removal assessment
https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/125260
title: Bulge formation of liquid film at the trailing edge: Scaling laws and particle removal assessment abstract: We present numerical simulations and laboratory experiments to study bulge formation at the trailing edge of an inclined surface and its inhibitory effect on particle removal during surface cleaning. We investigate the spatial variations in liquid films near the trailing edge and find that the Weber number can be used as a dominant parameter to determine bulge occurrence over the trailing edge. We divide the film region near the trailing edge at which the bulge occurs into two: the region where the surface linearly grows and the surface tension is negligible, and the region where the surface tension force becomes dominant and the film surface is curved. In the investigated cases in which the Reynolds number is O(10) or greater, the viscous forces are negligible, which allows for the derivation of the scaling laws for the length of the two regions according to the condition that the bulge height scales with the capillary length. In the resulting scaling law, the length scales depend on the Froude number and the inclination angle. The proposed scaling law allows for the prediction of the bulge shape and the prediction agrees with the simulation results, particularly at low Weber numbers (i.e., We < 0.5). Moreover, we construct a particle removability map to assess the removal of particles of different sizes at specific locations on the substrate. The map reveals a reduction of the removability for small-size particles or particles located in the bulge.
<br>Accurate hybrid AUSMD type flux algorithm with generalized discontinuity sharpening reconstruction for two-fluid modeling
https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/125259
title: Accurate hybrid AUSMD type flux algorithm with generalized discontinuity sharpening reconstruction for two-fluid modeling abstract: This paper presents a single-pressure-field two-fluid model with finite-volume discretization to solve the equations of motion of compressible multiphase flows. To capture the discontinuities caused by shock waves and fluid interfaces, we propose a generalized discontinuity sharpening technique that combines the conventional monotonic upstream scheme for conservation law (MUSCL) and tangent of hyperbola interface capturing (THINC) schemes. In addition, a slope ratio-weighted parameter, ζ, is used to control the proportion of values reconstructed by MUSCL and THINC, and we show that the present method can retain sharp interfaces when the value of the parameter β in the THINC scheme is set ranging from 1.6 to 3.0. Fluxes across various interfaces are evaluated using a hybrid AUSMD-type flux algorithm, where the mass flux and pressure induced on the cell faces are calculated using an approximate Riemann solver. The accuracy and robustness of the proposed method are validated by solving a series of one- and two-dimensional single-phase flows. Furthermore, complex wave patterns arising from two-dimensional shock bubble/water-column interactions are examined, which indicate that compared with the existing schemes applied to two-fluid modeling, the proposed scheme significantly sharpens the interfaces and captures more details of the flow features. Finally, simulations of a three-dimensional example of the liquid jet crossflow are conducted. The proposed scheme shows more details of the fluid interface, including the interfacial instabilities on the windward side of the liquid jet and droplet formation due to the breakup phenomenon in the downstream of the crossflow, than the existing schemes.
<br>An Experimental and Numerical Study on the Cavitation and Spray Characteristics of Micro-Orifice Injectors under Low-Pressure Conditions
https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/125144
title: An Experimental and Numerical Study on the Cavitation and Spray Characteristics of Micro-Orifice Injectors under Low-Pressure Conditions abstract: A fuel injector plays a crucial role in an internal combustion engine, and the occurrence of cavitation inside the injector may affect the engine’s spray characteristics, atomization characteristics, and combustion efficiency. Most literature investigated the cavitation characteristics for a micro-orifice injector under high injection pressure (P_inj) or a large-orifice injector under low P_inj, i.e., under high Reynolds number (Re). In this study, a micro-turbojet engine with a 0.3-mm-diameter micro-orifice fuel injector was developed for operation under low P_inj. The cavitation and spray characteristics of water and kerosene fuel in this injector were experimentally and numerically investigated. The results indicated that the water and kerosene also exhibited no cavitation, cavitation, super-cavitation, and hydraulic flip phenomena. However, the discharged jet was unaffected by the internal flows, and the jet angles remained approximately constant, implying that the cavitation in micro-orifice injectors under low Re is less important than that under high Re. Since the cavitation in micro-orifice injectors under low Re is not beneficial to the atomization and spray, the selection of geometry of the micro-injector is important. A micro-orifice injector with a small length-to-diameter (L/D) ratio of the injector nozzle has a rounded-edge inlet and a small taped angle due to the limitation of electrical discharge machining, which results in a high discharge coefficient and increases the difficulty of hydraulic flip. Thus, an L/D ratio of 3 is recommended for the injector of the developed micro-turbojet engine. This study provides some insights for the design of micro-turbojet engines.
<br>Analysis of a wind-driven power generation system with root slapping mechanism
https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/125102
title: Analysis of a wind-driven power generation system with root slapping mechanism abstract: This study introduces a groundbreaking slap-type Vibration Energy Harvesting (VEH) system, leveraging a rotating shaft with magnets to induce vibrations in an adjacent elastic steel sheet through magnetic repulsion. This unique design causes the elastic sheet to vibrate, initiating the oscillation of a seesaw-type rigid plate lever. The lever then slaps a piezoelectric patch (PZT) at the elastic steel sheet’s root, converting vibrations into electrical energy. Notably, the design enables the PZT to withstand deformation and flapping forces simultaneously, enhancing power conversion efficiency. The driving force for the rotating shaft is harnessed from the downstream flow field generated by moving objects like rotorcraft, fixed-wing aircraft, motorcycles, and bicycles. Beyond conventional vibration energy harvesting, this design taps into additional electric energy generated by the PZT’s slapping force. This study includes mathematical modeling of nonlinear elastic beams, utilizing the Method of Multiple Scales (MOMS) for in-depth vibration mode analysis. Experimental validation ensures the convergence of theory and practice, confirming the feasibility and superior voltage generation efficiency of this slap-type VEH concept compared to traditional VEH systems.
<br>熱力學(二)
https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/124956
title: 熱力學(二)航空複合材料層板嵌補式修補模擬分析之研究
https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/124935
title: 航空複合材料層板嵌補式修補模擬分析之研究 abstract: 複合材料具有強度高重量輕之特性,已隨著製程技術的成熟而被大量使用;近年來不管是軍機、民航機機身甚至是風力發電機台葉片都能看到複合材料的身影,而複合材料修復也成為未來需要面對的問題。本研究以嵌補式修補工法應用於碳纖維層板修復作為研究方向,為了探討橢圓嵌補塊修復複合材料層板之可行性,本研究以嵌補比和橢圓偏心率為修補塊設計考量。本研究使用有限元素分析軟體輔助嵌補塊尺寸設計,並透過三點彎曲試驗的最大變形量作為比較層板在修補前後的強度標準,發現當嵌補比為30之試片具有最小的變形量。本研究以嵌補比30作為橢圓嵌補塊尺寸設計,再進一步探討不同橢圓偏心率對修復層板抗彎曲負載程度的影響。
<br>小型探空火箭之可載荷門式鼻錐
https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/124849
title: 小型探空火箭之可載荷門式鼻錐 abstract: 一種小型探空火箭之可載荷門式鼻錐,其包含一主體、一活動半錐部、一磁吸組件、一彈性件及一活動閂組件;主體包括一底座與一固定半錐部;活動半錐部樞設於固定半錐部之一側,活動半錐部具有一閂孔;彈性件設置於固定半錐部;活動閂組件包括一閂體與一驅動件,閂體被驅動件驅動可凸伸於底座頂面或縮入底座;固定半錐部與活動半錐部接觸時藉由磁吸組件相互磁吸,彈性件被壓縮,閂體上升且插設於閂孔內,當閂體被驅動縮入底座內時,彈性件將活動半錐部推開後,閂體再被驅動上升凸伸於底座之頂面,以阻止活動半錐部與固定半錐部接觸。
<br>description: 專利證號:I825716
<br>具集風罩垂直軸阻力型風發電機空氣動力特性最佳化之數值研究
https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/124784
title: 具集風罩垂直軸阻力型風發電機空氣動力特性最佳化之數值研究 abstract: 作為綠能的一種,風能因取之不盡且無汙染,為取代傳統石化燃料的重要替代能源之一。風力發電機作為擷取風能並轉換為電能的主要裝置,因此風機的操作性能直接影響到風能的轉化率。因風機的功率係數(CP)與轉子的轉速成正比,因此具有高轉速特性的風機,表示具有較佳之操作性能。本研究以CFD軟體FlowVision模擬具集風罩之垂直軸阻力型風力發電機,並以田口法求得風機的最佳參數,使風機具有最高的轉速。
模擬之風機,其轉子直徑3.5公分、高29公分,集風罩內徑6公分、外徑64.2公分、高31公分。控制因子為轉子的葉片直徑大小(5公分、6.7公分、8.375公分)、轉子的葉片數(6、8、10片),和集風罩的導片數(6、8、10片),並將風速(8m/s及4m/s)作為干擾因子。本研究選用L_9 (3^4 )直交表規劃實驗條件,並利用因子水準反應分析,探討各控制因子對風機轉速的重要性。
結果顯示葉片直徑8.375公分、8葉片數及6導片數為最佳水準組合,在風速8m/s及4m/s的情況下,轉速分別為464.57RPM及227.66RPM。經由因子水準反應分析,三個參數中,集風罩的導片數對實驗結果的影響最大,其次是轉子的葉片數,最後是轉子葉片直徑大小。使用田口法的加法模式預測各實驗條件的轉速,再與數值模擬計算所得之轉速比較,誤差皆小於0.2%,顯示田口法所獲得之模型具有想當可性度。挑選由田口法分析所得之最佳與最差兩種水準組合,比較在風速8m/s條件下的CP-TSR如上圖,顯見經最佳化參數後,風機性能的提升。兩種水準組合條件下的速度流場如下圖。
<br>風力獵能系統
https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/124694
title: 風力獵能系統 abstract: 一種風力獵能系統,包括一可旋轉風車、至少一突出單元、一第一彈片單元、一第二彈片單元與一第一固定單元。可旋轉風車,由風力驅動旋轉,並具有軸套部。至少一突出單元,形成於軸套部上,用以安裝第一磁鐵件。第一彈片單元,其一端安裝有與第一磁鐵件相異磁性之第二磁鐵件。第二彈片單元,與第一彈片單元相鄰,第二彈片單元的一端安裝有一壓電材料。第一固定單元,用以分別與第一彈片單元、第二彈片單元的另一端連接。當可旋轉風車旋轉時,同步帶動第一磁鐵件旋轉,且第二磁鐵件受第一磁鐵件之磁力影響帶動第一彈片單元擺動,並拍擊壓電材料產生形變而形成電訊號。
<br>description: 專利證號:I806713
<br>Energy harvesting analysis of the magneto-electric and fluid-structure interaction parametric excited system
https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/124677
title: Energy harvesting analysis of the magneto-electric and fluid-structure interaction parametric excited system abstract: This research proposes an innovative design of a fluid-solid coupling vibration energy harvesting
system (VEH system) that includes a downstream waterwheel driven by the flow field, which, in
turn, drives gears and connecting rods to rotate a wheel equipped with magnets to generate
electricity by changing the magnetic field. A piezoelectric patch (PZT) is installed upstream of the
pipeline with a magnet attached to it. The repulsive force between the magnet on the wheel and
the magnet on the PZT generates additional force while also creating vibration through fluid-solid
coupling of the pipeline. The study derives a theoretical model of the nonlinear vibrating beam
and couples it with the piezoelectric and magneto-electric equations to simulate the vibration of
the fixed-fixed elastic pipe. The method of multiple scales (MOMS), fixed points plots, phase plots,
and Poincar´e maps are employed to verify the theoretically predicted parametric excitation
properties of the system. The study uses the Biot-Savart Law to calculate the theoretical magnetic
force and combines it with the fluid-conveying nonlinear beam and the PZT to create a magnetoelectric
coupling fluid pipeline vibration energy harvesting model. The study conducts a simple
experiment to verify the feasibility of the theoretical model and demonstrates that the repulsive
force of the magnet significantly enhances the electric generation benefit of the system.
Regardless of whether the PZT is located in the curved or flat area (straight part) of the nonlinear
beam, the addition of magnets to the system significantly increases voltage generation efficiency
by more than 190 % when compared to systems without magnets.
<br>Predicting Multiple Numerical Solutions to the Duffing Equation Using Machine Learning
https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/124676
title: Predicting Multiple Numerical Solutions to the Duffing Equation Using Machine Learning abstract: This study addresses the problem of predicting convergence outcomes in the Duffing
equation, a nonlinear second-order differential equation. The Duffing equation exhibits intriguing
behavior in both undamped free vibration and forced vibration with damping, making it a subject
of significant interest. In undamped free vibration, the convergence result oscillates randomly between
1 and −1, contingent upon initial conditions. For forced vibration with damping, multiple
variables, including initial conditions and external forces, influence the vibration patterns, leading
to diverse outcomes. To tackle this complex problem, we employ the fourth-order Runge–Kutta
method to gather convergence results for both scenarios. Our approach leverages machine learning
techniques, specifically the Long Short-Term Memory (LSTM) model and the LSTM-Neural Network
(LSTM-NN) hybrid model. The LSTM-NN model, featuring additional hidden layers of neurons,
offers enhanced predictive capabilities, achieving an impressive 98% accuracy on binary datasets.
However, when predicting multiple solutions, the traditional LSTM method excels. The research
encompasses three critical stages: data preprocessing, model training, and verification. Our
findings demonstrate that while the LSTM-NN model performs exceptionally well in predicting
binary outcomes, the LSTM model surpasses it in predicting multiple solutions.
<br>Enhancing Electrical Generation Efficiency through Parametrical Excitation and Slapping Force in Nonlinear Elastic Beams for Vibration Energy Harvesting
https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/124675
title: Enhancing Electrical Generation Efficiency through Parametrical Excitation and Slapping Force in Nonlinear Elastic Beams for Vibration Energy Harvesting abstract: This study aims to enhance conventional vibration energy harvesting systems (VEHs) by
repositioning the piezoelectric patch (PZT) in the middle of a fixed–fixed elastic steel sheet instead
of the root, as is commonly the case. The system is subjected to an axial simple harmonic force at
one end to induce transversal vibration and deformation. To further improve power conversion,
a baffle is strategically installed at the point of maximum deflection, introducing a slapping force
to augment electrical energy harvesting. Employing the theory of nonlinear beams, the equation
of motion for this nonlinear elastic beam is derived, and the method of multiple scales (MOMS)
is used to analyze the phenomenon of parametric excitation. This study demonstrates through
experiments and theoretical analysis that the second mode yields better power generation benefits
than the first mode. Additionally, the voltage generation benefits of the enhanced system with the
added baffle (slapping force) surpass those of traditional VEH systems. Overall, the proposed model
proves feasible and holds promising potential for efficient vibration energy harvesting applications
in various industrial sectors.
<br>利用熱電晶片除濕與回收技術應用於家用烘乾機之節能效益研究
https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/124612
title: 利用熱電晶片除濕與回收技術應用於家用烘乾機之節能效益研究 abstract: 本研究利用熱電冷凝冷回收式除濕和熱交換器除濕與熱回收的方法,分別對於家用高耗電量的電器設備進行節能效益研究。
對於熱電冷凝冷回收除濕實驗,首先探討除濕系統於自然對流式除濕系統與強制進氣式冷回收除濕系統進行性能比較,透過本研究冷回收通道的設計,以強制進風的方式,將通過冷端鰭片之低溫空氣回收利用,並透過風扇將低溫空氣全部導入熱端鰭片對其進行輔助散熱,此方法不但能提高熱端的散熱能力,使冷端鰭片冷凝能力提升,亦能降低除濕機出口排放溫度,減少室內因需長期除濕而使空間溫度升高,又得開啟空調降溫至人體舒適溫度所額外消耗過量的電力。而針對冷凝面下方的滴狀冷凝研究,本研究提出冷凝面傾斜特殊的角度與除濕效率之間的相關性,實驗當中分別透過非垂直的四種不同的鰭片傾斜角度(〖38〗^o 、〖52〗^o 〖、66〗^o 〖、80〗^o)進行冷凝液滴形成現象進行分析與其除濕量之比較。最後為熱回收技術實驗,本研究使用熱交換器與熱回收裝置,針對高耗能與排放廢熱量高的烘乾機進行實驗,實驗方法為將烘乾機排出的高溫高濕氣體,利用熱交換器將排出的氣體進行除濕,同時引進外氣進行預熱,最後將兩種氣體搭配熱回收控制系統進行混合與最佳比例的調配,並利用國際對於烘乾機認證的性能指標-單位能耗除濕量(Specific Moisture Extraction Rate)進行計算,進行性能比較。
由實驗結果可知,強制進風冷回收式除濕系統,比自然對流無冷回收式系統提升48.8%的除濕量。而傾斜式冷凝方面,在冷端鰭片傾斜角度在〖52〗^o時有最佳的除濕量,又與強制進風垂直式除濕系統相比,能更提升7.5% 的除濕量與減少11%的出風口溫度,且一天總耗電量僅為1.3度,非常具有節能特色。而對於熱回收除濕技術方面,加裝熱交換器的烘乾性能SMER值比未加裝前還低19%。實驗再將其結合熱回收裝置進行實驗,結果顯示,當除濕後的排氣與預熱後的外氣回收混合比例為6:4的時候,系統呈現出最佳及最低的烘乾性能指標SMER值 (1.086),其節約電量百分比亦高達最佳的18%。
This study investigated the energy efficiency of high energy-consuming appliances by examining thermoelectric cooling, cold-recovery condensation dehumidification as well as a heat exchanger’s dehumidification and heat recovery.
To conduct an experiment for the thermoelectric, cold-recovery condensation dehumidification, this study first compared the performance of a dehumidifier based on natural convection and a cold-recovery dehumidifier based on forced air intake. In the study’s cold-recovery channel, forced air intake was employed to recover and reuse the low-temperature air passing the evaporator; then, a fan was used to transfer the low-temperature air into the condenser to remove the heat in the condenser. This method improved the heat removal, enhanced the condensation by the evaporator, and reduced the temperature of outlet air from the dehumidifier, thereby eliminating the problem of excessive electricity used by air-conditioning system. This mitigate the problem of additional electricity used by air-conditioning systems for reducing the increased indoor temperature, which is caused by continuous dehumidification for a long time, to a comfortable range for human body. Investigating on the condensed drips below the evaporator, this study proposed a correlation between the tilt angle of the evaporator and the dehumidification efficiency. An experiment was conducted by analyzing the drip condensation and comparing the dehumidification performance of the dehumidifier when its evaporator was positioned in four different angles, namely 38°, 52°, 66°, and 80°.
In terms of heat recovery, this study used a heat exchanger and heat-recovery device in an experiment on appliances exhibiting high energy consumption and waste heat. In the experiment, a heat exchanger was used to dehumidify the high-temperature and humid air exhausted from a dryer; concurrently, ambient air was drawn to the heat exchanger and preheated. Then, the two types of air were mixed in various ratios by using a heat-recovery device to identify the optimal amount of heat recovery. The specific moisture extraction rate (SMER), an international performance indicator for dryers, of the dryer was calculated to analyze its performance.
According to the experimental results, the forced-air-intake cold-recovery dehumidifier achieved a higher amount of dehumidification than the natural-convection dehumidifier without cold recovery by 48.8%. Regarding the tilt angle of evaporator, the dehumidifier with an evaporator tilt angle of 52° achieved optimal dehumidification efficiency and, compared with the forced-air-intake dehumidifier whose evaporator was positioned vertically, exhibited a higher amount of dehumidification and a lower temperature of outlet air by 7.5% and 11%, respectively. Additionally, the dehumidifier with an evaporator tilt angle of 52° was highly capable of energy saving, consuming only 1.3 kWh a day. With regards to the heat recovery method, the dryer’s SMER was reduced by 19% after it was installed with a heat exchanger. The experimental results also revealed that, in the dryer installed with a heat-recovery device, the optimal SMER (1.086) and percentage of electricity saved (18%) were achieved when the mixing ratio of the dehumidified air exhausted by the dryer to the preheated air collected from the ambient air was 6:4.
<br>An Aerodynamic Reinvestigation of the Hydroplaning Phenomenon
https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/124589
title: An Aerodynamic Reinvestigation of the Hydroplaning Phenomenon abstract: In this work we implement software to investigate the aerodynamics of hydroplaning phenomenon on an isolated wheel. The isolated wheel, Fackrell’s A2 wheel is the most common used benchmark and is applied here, and since the wheel is contact with the ground, the geometric setup of contact patch is rather important in our simulation in order to prevent the high skewness grid situation. Our results of C_L and C_D of A2 wheel model comparing with experiment results are all under 1% error. Also, our simulation of hydroplaning phenomenon utilizes the Volume of Fluid (VOF) method to simulate this two-phase flow problem. Although using different numerical approach, our results show that the current hydroplaning model is qualitatively and quantitatively similar to the results of earlier works. Furthermore, we might claim that innovative and straight forward approaches to simulate the dynamic hydroplaning phenomenon have been achieved.
<br>Experimental study on air extraction performance of novel rooftop natural ventilators
https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/124441
title: Experimental study on air extraction performance of novel rooftop natural ventilators abstract: The air extraction performance of novel rooftop natural ventilators was experimentally investigated and compared to the conventional turbine ventilator. The newly developed ventilator integrates a vertical-axis wind turbine with a static ventilator, where the wind turbine, equipped with 8 C-type rotors and 6 rotor guide vanes, serves to drive the rotation of the static ventilator. The static ventilator is an exhaust cowl with curved guide vanes inside. The wind turbine, including 8 C-rotors and 6 flat guide vanes, is 10 cm in height with a diameter of 21 cm. The dimensions of static ventilation are 7 cm in height, and 26 cm and 21 cm in bottom and top diameters, respectively, with curved guide vanes inside. Various heights of guide vanes (0.5 cm and 3 cm) and numbers of guide vanes (0, 6, and 12) were investigated. An open wind tunnel system was used to simulate the condition where the wind blows over the rooftop ventilator. The ventilator air extraction rates were determined using the mean air velocities, measured using a hot-wire anemometer at an open slot in a ventilation pipe connected to the ventilator. The results indicated that the rotating and non-rotating novel ventilators exhibited superior air extraction rates at most tested wind speeds compared to the rotating conventional turbine ventilator. The curved guide vanes inside the static ventilator played the most important role in the air extraction rate. This study suggests that a static ventilator with an adequate guide-vane design may be more suitable for rooftop ventilation than a conventional turbine ventilator.
<br>Simulation of the effects of dilution gas for the formation of CJ plane during the oblique detonation
https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/124295
title: Simulation of the effects of dilution gas for the formation of CJ plane during the oblique detonation abstract: This study aims to properly simulate transition patterns (the initiation structure between oblique shock wave and oblique detonation wave) to better understand the performance of oblique detonation wave engines under practical operating conditions. The former two cases are observed in a stoichiometric hydrogen-air mixture, the oblique detonation originates from the impact shock region where the pre-combustion hot gas near the wall interacts with the oblique shocks. In the second case, different proportions of dilution gas are tested. It is noted that a thermal choking condition due to strong compression waves during a sufficient duration results in the turning transverse waves and the inhomogeneous Chapman–Jouguet (CJ) plane. Therefore, the deformed CJ plane, the nonuniform combustion structures, and the overheated oblique detonation wave (ODW) with the excessive pressure rise are shown. Finally, it is concluded that the chemical equilibrium shift and the stability of ODW in the combustor are significantly affected by the expanding flow of dilution gases.
<br>Accurate simulation of discontinuities induced by detonations
https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/124294
title: Accurate simulation of discontinuities induced by detonations abstract: In this study, we propose the HMSTH (Hybrid MUSCL with THINC-EM) [6, 11] type AUSMD [5] flux scheme to solve the stiff Euler equations to achieve an accurate simulation of the detonation waves. When the detonation wave propagates downstream after being ignited in the combustion, it produces a supersonic wave through the nozzle to achieve the thrust cycle called the Pulse Detonation Engine (PDE). [10] The PDE has a great advantage in energy efficiency according to many studies, so its development is important in the future. To overcome the applicant issue making the PDE work smoothly. We work to build an appropriate numerical method. To verify it, one and two-dimensional shock tube problems and the PDE combustion are chosen as the benchmark cases. The numerical results show that the proposed HMSTH-type AUSMD scheme has great potential in simulating further complicated detonation waves and PDE problems.
<br>Development of a Lagrangian–Eulerian approach-based five-equation two-fluid model for simulation of multiphase reactive flows
https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/124293
title: Development of a Lagrangian–Eulerian approach-based five-equation two-fluid model for simulation of multiphase reactive flows abstract: The purpose of the current study is to develop numerical capability to analyze the flow structures of the scramjet engine in which many complex physical phenomena are involved, such as shock waves, breakup, atomization, and chemical reactions. To understand these complex physical phenomena, we first proposed the five-equation multiphase flow model coupling with the Lagrangian method to reproduce the process of fuel atomization and evaporation in a flow over a side jet problem. Shock waves, recirculation zones, and breakup processes of droplet particles were well captured in the computational works. It was shown that the five-equation multiphase model achieved better resolution of the shock-capturing comparing with the single-phase Navier–Stokes equation coupling with the Lagrangian approach. In addition, the single-step reaction model was performed with the current five-equation multiphase model to simulate the detonative cell in the detonation flow problem. The detonation waves under various operating conditions were discussed. Finally, a preliminary simulation is applied to the flow phenomena through DLR scramjet. The current works have achieved satisfactory agreement compared to the experimental data no matter in reacting flow case or nonreacting flow case.
<br>Electron Dynamic Modelling during Dipolarization Substorm Events by Test Particle Simulations
https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/124142
title: Electron Dynamic Modelling during Dipolarization Substorm Events by Test Particle Simulations abstract: We developed a test particle simulation code to examine the electron dynamics during multiple dipolarization substorm events detected by the THEMIS mission. Through the Tao-Chan-Brizard guiding center model, we evaluated the trajectories of 0.1, 1, and 10 keV electrons with different initial pitch angles and L-shells. We applied the Tsyganenko model TS05 and the IGRF-12 to generate the time-varying magnetic field model with the corresponding inductive and polarized electric fields.
The particle flux and energy enhancements in the nighttime magnetosphere characterize dipolarization events. The increase in the magnetic field and the corresponding induced and polarized electric field energizes and transports the particles earthward, which can explain the mechanism of the particle flux enhancement in the inner magnetosphere.
<br>Whistler-Mode Wave Normal Angle Shift and the Related Pitch Angle Distribution of Electrons During Dipolarization
https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/124141
title: Whistler-Mode Wave Normal Angle Shift and the Related Pitch Angle Distribution of Electrons During Dipolarization abstract: A peculiar wave event was recorded in the whistler frequency range at around a few hundred Hz, at a
dipolarization site near the magnetic equator, about 10 Earth radii tailside. The THEMIS mission observed
this wave event during an intense decrease in the auroral electrojet index (AL). The wave event is unique,
with a shift in the wave normal angle from nearly 160o to 20o, right after the dipolarization angle reaches
its maximum. The effect of pitch angle scattering on electrons through cyclotron and Landau resonances
via this wave event is investigated by performing test particle simulations incorporating the observed wave
amplitudes and wave normal angles. The results showed that the primary scattering could occur at nearly
0 and 180 degrees for electrons around 10 keV, similar to the observed changes in electron pitch angle
distributions of a similar energy. We will present the observations and computations and show that a wave
event with shifted wave normal angles can cause changes in pitch angle distributions in different
directions with respect to the ambient magnetic field.
<br>以機器學習方法預估杜芬方程式的多重數值解
https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/123829
title: 以機器學習方法預估杜芬方程式的多重數值解ON THE AERODYNAMIC ANASYSIS OF A MODERN ALL-ELECTRIC POWERED CE-LINER AIRCRAFT
https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/123828
title: ON THE AERODYNAMIC ANASYSIS OF A MODERN ALL-ELECTRIC POWERED CE-LINER AIRCRAFT abstract: The Ce-Liner aircraft developed by Bauhaus Luftfahrt is selected as our research target, and the C-wing assembly is based on a non-planar three-surface configuration: main wing, side wing and top wing. This work implement software to simulate whether Ce-Liner can reduce the generation and strength of wingtip vortices during cruise, and whether it can improve the efficiency of the aircraft with better economic benefits. Our findings revealed this Ce-Liner configuration can increase the lift-to-drag efficiency by about 20 percent during cruise. Also since it’s an all-electric aircraft, it can greatly reduce the weights of the turbofan engine and fuel, thus the high-lift devices can be eliminated. Furthermore, this Ce-Liner will not need to stock fuel in the main wing, hence the thickness and weight of the wing could be further reduced. In addition, it is found that this aircraft configuration has a stronger crosswind resistance capability due to our gust crosswind simulation.
<br>AERODYNAMIC ANALYSIS OF AN ALL ELECTRIC POWERED BLENDED WING BODY AIRCRAFT WITH ANTI-BIRD STRIKE DEVICE
https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/123827
title: AERODYNAMIC ANALYSIS OF AN ALL ELECTRIC POWERED BLENDED WING BODY AIRCRAFT WITH ANTI-BIRD STRIKE DEVICE abstract: The objectives of this study are the aerodynamic analyses of an all-electric powered BWB configuration and the bird strike resistance net. This bird strike resistance net is made of porous material, in conic shape with 45 degree cone angle. Our major research findings are the invention of an all-electric fan engine with enough thrust produced for take-off and cruise conditions and a detailed investigation of BWB’s aerodynamic characteristics during cruise. It is found that we can achieve satisfactory aerodynamic efficiency with our BWB-electric engine-bird strike resistance net configuration; while current bird strike resistance net shape will not greatly affect the engine performance, this net will account for almost half of the overall engine’s drag or about 19% of BWB total drag.
<br>Design and programming of a stress intensity factor search platform
https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/123826
title: Design and programming of a stress intensity factor search platform結合粒子群與螢火蟲演算法於結構最佳化設計之研究
https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/123825
title: 結合粒子群與螢火蟲演算法於結構最佳化設計之研究 abstract: 本論文應用粒子群螢火蟲演算法於結構最佳化設計中。粒子群演算法為仿生演算法,其特點為收斂速度快,參數設定少、搜尋範圍廣泛及具有記憶性。螢火蟲演算則是模擬螢火蟲在求偶時使用亮光互相吸引,在空間中尋找最亮光源的特性來尋找問題的最佳解。螢火蟲演算法將區域中的各初始值模擬為各個螢火蟲個體,賦予各個體初始吸引值並依照光衰公式定義出吸引力關係式而推導出迭代關係式,使各值趨近於最佳解。粒子群螢火蟲演算法則是結合粒子群演算法和螢火蟲演算法兩種方法進行運算,利用螢火蟲演算法之光吸收強度特性增加區域搜尋效率,並透過粒子群演算法多點搜尋的能力加快收斂之速度。本研究結合兩種演算法的優點成一混合之演算法,以達到運算之效益並減少運算時間。數值範例中將對各種結構做分析與討論,結果顯示粒子群螢火蟲演算法能夠在結構最佳化取得不錯的成效。
<br>An assessment of whistlers generated from tree-like gigantic jets
https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/123231
title: An assessment of whistlers generated from tree-like gigantic jets abstract: The characteristics of whistlers generated from an observed gigantic jet (GJ) are assessed and possible locations to detect these waves are deduced. Modeling is based on disturbances in the electric field, as measured by NCKU ELF/VLF station, associated with a tree-like GJ event over typhoon Lionrock. The power spectrum of GJ differs from that of common cloud-to-ground lightning; therefore, this study also investigates differences between GJ-generated signals and common lightning-generated whistlers. Detectability is evaluated by considering the absorption of amplitudes resulted from collisional damping associated with the propagation of generated waves. Our results show that in the ionosphere the waves are subject to greater attenuation as the frequency increases; however, a reversal occurs at lower frequencies of a few hundred Hz. The calculated waveforms show that the whistlers generated by the tree-like GJs are preceded by small fluctuations at high frequencies generated by the initiating lightning. Overall, the amplitudes increase with the passage of time; however, they are more randomly-distributed over time for whistlers generated from common lightning. The amplitudes decrease again when lower-frequency components below a few hundred Hz arrive. The amplitudes drop to the order of 1 mV/m as the waves propagate in the ionosphere, which puts them within a range detectable by the instruments on most satellites. Based on the locations of tree-like GJ events observed by ISUAL (Imager of Sprites and Upper Atmospheric Lightning), regions of the western and southeastern Pacific Ocean, as well as northern Africa region are the most likely locations to detect these whistlers.
<br>Bulge formation of liquid film at the trailing edge: Scaling laws and particle removal assessment
https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/123230
title: Bulge formation of liquid film at the trailing edge: Scaling laws and particle removal assessment abstract: We present numerical simulations and laboratory experiments to study bulge formation at the trailing edge of an inclined surface and its inhibitory effect on particle removal during surface cleaning. We investigate the spatial variations in liquid films near the trailing edge and find that the Weber number can be used as a dominant parameter to determine bulge occurrence over the trailing edge. We divide the film region near the trailing edge at which the bulge occurs into two: the region where the surface linearly grows and the surface tension is negligible, and the region where the surface tension force becomes dominant and the film surface is curved. In the investigated cases in which the Reynolds number is O(10) or greater, the viscous forces are negligible, which allows for the derivation of the scaling laws for the length of the two regions according to the condition that the bulge height scales with the capillary length. In the resulting scaling law, the length scales depend on the Froude number and the inclination angle. The proposed scaling law allows for the prediction of the bulge shape and the prediction agrees with the simulation results, particularly at low Weber numbers (i.e., We < 0.5). Moreover, we construct a particle removability map to assess the removal of particles of different sizes at specific locations on the substrate. The map reveals a reduction of the removability for small-size particles or particles located in the bulge.
<br>Numerical study of optimum parameter design for film cooling effectiveness by Taguchi method
https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/123229
title: Numerical study of optimum parameter design for film cooling effectiveness by Taguchi method abstract: The present numerical study investigated a novel film cooling scheme that combines a cylindrical hole with an upstream Barchan-dune ramp and a triangular tab over the hole. Simulations revealed that this arrangement can induce an additional anti-kidney vortex pair on the outside of the original primary kidney vortices to suppress the penetration of the high-temperature mainstream by the cooling flow, increasing cooling effectiveness. Compared with schemes employing only a triangular tab or a Barchan-dune ramp, the novel film cooling scheme achieved superior cooling performance. An optimum parameter design is determined through the Taguchi method. Three parameters were investigated, namely, the Barchan-dune-shaped ramp height, triangular tab length, and blowing ratio, under various incoming temperatures. Analysis of variance revealed that the blowing ratio has the greatest influence on cooling effectiveness. An average cooling effectiveness of 34.1% was achieved by the optimum parameter design.
<br>Analysis of double inverted flag energy harvesting system in pipe flow
https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/123228
title: Analysis of double inverted flag energy harvesting system in pipe flow abstract: This technical note numerically and experimentally studies a vibration energy harvester (VEH) consisting of a set of two parallel elastic steel sheets (ESSs) and piezoelectric patches (PZTs) in pipe flow. The roots of the elastic steel sheets are fixed on the base with the PZTs to form a double inverted flag vibration energy harvesting system (DIF-VEHS). In this note, a semi-circular receiving device (receiver) was added to the free end of the elastic steel, and a cylinder was installed upstream to generate a periodic oscillating flow field in the pipeline to obtain better electric energy generation efficiency. This study reveals the effect of different factors on the energy harvesting system, such as the distance between the ESSs, the diameter of the cylinder, etc. This study uses ANSYS software to simulate the fluid–structure interaction vibration of ESSs to determine the feasibility of this design. An experimental setup is then implemented to find the most effective combination of factors for the system. The results of this study show that with all parameters configured properly, the electric energy generation reaches a maximum average value of 1.6657 V per minute. In the future, such devices could be installed in sewers, pipes or rivers, allowing the flow energy of the fluid to be recycled to generate more energy.
<br>Analysis of a Clapping Vibration Energy Harvesting System in a Rotating Magnetic Field
https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/123227
title: Analysis of a Clapping Vibration Energy Harvesting System in a Rotating Magnetic Field abstract: This technical note proposes a clapping vibration energy harvesting system (CVEH system) installed in a rotating system. This device includes a rotating wheel, a drive shaft that rotates the wheel, and a double elastic steel sheet fixed on the drive shaft. One of the free ends of the steel is fixed with a magnet, and the free end of the other elastic steel is fixed with a PZT patch. We also install an array of magnets on the periphery (rim) of the wheel. The rim magnets repulse the magnet on the elastic steel sheet of the transmission shaft, causing the elastic steel to oscillate periodically, and slap the piezoelectric patch installed on the other elastic steel sheet to generate electricity. In this study, the authors’ previous study on the voltage output was improved, and the accurate nonlinear natural frequency of the elastic steel was obtained by the dimensional analysis method. By adjusting the rotation speed of the wheel, the precise frequency was controlled to accurately excite the energy harvesting system and obtain the best output voltage. A simple experiment was also performed to correlate with the theoretical model. The voltage and power output efficiencies of the nonlinear frequency to linear frequency excitation of the CVEH system can reach 15.7% and 33.5%, respectively. This study confirms that the clapping VEH system has practical power generation benefits, and verifies that nonlinear frequencies are more effective than linear frequencies to excite the CVEH system to generate electricity.
<br>Vibration reduction of continuous moving loads on a nonlinear simple beam resting on an elastic foundation
https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/123226
title: Vibration reduction of continuous moving loads on a nonlinear simple beam resting on an elastic foundation abstract: This technical note investigates a hinged-hinged nonlinear Euler-Bernoulli beam resting on an elastic foundation subjects to moving loads. The method of multiple scales (MOMS) is employed to analyze this nonlinear beam model. The fixed points plots are made to identify the system’s internal resonance. The frequency ratio plot is proposed to predict the system internal resonance conditions. This study improved the author’s earlier work for a wider range of prediction on internal resonance conditions. The continuous concentrated moving loads are applied to this nonlinear beam model. The dynamic vibration absorber (DVA) is attached on the beam to reduce vibration and prevent internal resonance. The mass, spring constant and location of the DVA are studied to obtain the best damping effect on the nonlinear beam with moving loads. The results are verified by numerical results and ANSYS simulations.
<br>航空材料學
https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/122841
title: 航空材料學熱力學(一)
https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/122840
title: 熱力學(一)Fermi acceleration of electrons driven by electric fields coupled to curvature drifts during dipolarization
https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/122771
title: Fermi acceleration of electrons driven by electric fields coupled to curvature drifts during dipolarization abstract: The pitch angle distributions (PADs) of electrons have shown variations due to the changes in field configurations during dipolarization via satellite observations at Earth’s tailside. A specific variation of energy-dependent pattern for the associated field-aligned anisotropies η was also often found from tens of eV to hundreds of eV or from hundreds of eV to thousands of eV during dipolarization by measurements of the instrument ESA (ElectroStatic Analyzer) for < 30keV electrons onboard of THEMIS Mission. In the beginning of dipolarization, a distinct peak of η occurred at a lower energy level; during dipolarization, a peak with smaller value occurred at a higher energy level. Two representative events at 10 Earth radii will be presented. One event showed an increase in differential energy fluxes above ~ 2keV while the other event showed a decrease in these fluxes above a similar energy level. Fermi acceleration of electrons driven by electric fields coupled to curvature drifts is examined by adopting the values of observed electric fields and magnetic fields. Interestingly, deceleration of electrons is found possible to occur through inputting the real observed values of electric/magnetic fields, though this mechanism was used to theoretically explain electrons accelerated to high energies at the presence of a dawn-to-dusk electric field. Therefore, this Fermi acceleration/deceleration is found to yield larger η at higher energy levels closer to observed range as well as produce the observed increase/decrease in changes of differential energy flux above ~ 2keV. This can be considered as the scientific benefit from observations besides theoretical works.
<br>應用於輕航機翼之碳纖維複合材料層板修補強度與模擬分析比較之研究
https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/122558
title: 應用於輕航機翼之碳纖維複合材料層板修補強度與模擬分析比較之研究灰狼演算法於無人飛行載具結構最佳化設計之研究
https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/122509
title: 灰狼演算法於無人飛行載具結構最佳化設計之研究 abstract: 本計劃是應用灰狼演算法、拓樸最佳化與B-spline函數於無人飛行載具結構件最佳化外形設計之研究。灰狼演算法是較為新穎的演算法,受到灰狼掠食行為啟發,狼群有非常嚴格的階級制度,階級高的狼帶領階級低的狼進行跟蹤、包圍、追捕,攻擊的掠食行為,一步一步接近獵物,類似最佳化設計中的尋找。灰狼演算法有著優秀的全域搜尋能力,設定參數少,收斂速度快,所以有著廣泛的運用。計劃中將使用ANSYS做為結構分析的工具,並利用拓樸設計方法中之最佳材料分配法作為拓樸最佳化方法。在本研究中除使用混合法同時保留必要元素與排除非必要元素來減少不合理之情形外,並應用B-spline函數之概念,設計移動限制來定義設計參數上下限以平滑結構外形。本研究採用多階段拓樸最佳化的方法,在階段拓樸最佳化後逐步的減少設計變數,可以減少電腦之計算時間。經過多階段拓樸最佳化設計後,可改善傳統拓樸最佳化設計結果不平滑之現象,以達到更具實用性之結構最佳外形設計。為了減輕無人機結構重量,提高飛機效能,以往小型無人機皆以複合材料搭配巴爾莎木或者航空合板製成,航空合板常用在不需要強度要求的機肋製造。3D列印機是一種快速成形的技術,通過多層列印的方式去構造出零組件,本計畫準備應用3D列印機印製無人機拓樸最佳化設計零組件結構。
<br>description: 計畫編號:MOST 109-2221-E-032-009
<br>Accurate hybrid AUSMD type flux algorithm with generalized discontinuity sharpening reconstruction for two-fluid modeling
https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/122467
title: Accurate hybrid AUSMD type flux algorithm with generalized discontinuity sharpening reconstruction for two-fluid modeling abstract: This paper presents a single-pressure-field two-fluid model with finite-volume discretization to solve the equations of motion of compressible multiphase flows. To capture the discontinuities caused by shock waves and fluid interfaces, we propose a generalized discontinuity sharpening technique that combines the conventional monotonic upstream scheme for conservation law (MUSCL) and tangent of hyperbola interface capturing (THINC) schemes. In addition, a slope ratio-weighted parameter, ζ, is used to control the proportion of values reconstructed by MUSCL and THINC, and we show that the present method can retain sharp interfaces when the value of the parameter β in the THINC scheme is set ranging from 1.6 to 3.0. Fluxes across various interfaces are evaluated using a hybrid AUSMD-type flux algorithm, where the mass flux and pressure induced on the cell faces are calculated using an approximate Riemann solver. The accuracy and robustness of the proposed method are validated by solving a series of one- and two-dimensional single-phase flows. Furthermore, complex wave patterns arising from two-dimensional shock bubble/water-column interactions are examined, which indicate that compared with the existing schemes applied to two-fluid modeling, the proposed scheme significantly sharpens the interfaces and captures more details of the flow features. Finally, simulations of a three-dimensional example of the liquid jet crossflow are conducted. The proposed scheme shows more details of the fluid interface, including the interfacial instabilities on the windward side of the liquid jet and droplet formation due to the breakup phenomenon in the downstream of the crossflow, than the existing schemes.
<br>Effects of secondary diffractions on the stress intensity factors generated for a finite crack in magneto-electroelastic materials
https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/122445
title: Effects of secondary diffractions on the stress intensity factors generated for a finite crack in magneto-electroelastic materials應力強度因子搜尋平台之建構與程式設計
https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/122338
title: 應力強度因子搜尋平台之建構與程式設計 abstract: 在破壞力學中,應力強度因子可用於預測脆性材料之裂紋尖端附近的應力場,作為判斷裂紋是否擴大的依據,為線彈性破壞力學中計算損傷容忍度的一大基礎,被廣泛應用於飛機、火箭、橋樑、核反應爐以及運輸工具等結構上。現今,大多數的應力強度因子皆可透過手冊查詢到相對應的結果,但由於手冊眾多,且紀錄形式多為紙本資料,蒐集及翻閱資料的過程不僅十分麻煩還會花費大量的時間
。此外,許多手冊的年代久遠,其內容已經不能滿足使用者的需求,又難以取得。因此,本研究結合Visual Studio C# 2019以及MySQL資料庫設計一個搜尋平台,用以彙整現有的手冊、期刊、會議紀錄等文獻內應力強度因子相關的內容,並提供使用者透過點選篩選條件或是輸入關鍵字的方式快速地查詢所需的資料。
<br>description: 計畫編號:MOST 109-2221-E-032-007
<br>應用於輕航機機翼之碳纖維複合材料層板修補強度與模擬分析比較之研究
https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/122290
title: 應用於輕航機機翼之碳纖維複合材料層板修補強度與模擬分析比較之研究 abstract: 複合材料近年來在航空界運用的比例越來越多,因為質量輕及抗腐蝕性佳等特性,已經逐漸取代過去常見金屬材料。本研究的研究目的是將碳纖維複合材料運用於輕航機機翼上,根據機翼損壞位置並透過修補過後的結構強度分析是否與完整碳纖維層板相同;利用真空加壓成型法,製作出3片共8層碳纖維層板,將3片碳纖維層板進行強度測試,以確認修補過後的碳纖維是否和完整無破損的碳纖維層板承受相同強度壓力測試。透過非破壞性超音波檢測是否有修補正確,也能清楚地得知脫層以及裂縫位置,再運用有限元素套裝軟體模擬加壓並分析完整碳纖維層板的應力與結構強度,最後將模擬結果與分析結果兩者進行比較,分析誤差是在合理的範圍內,希望未來能夠應用更大量碳纖維複合材料在輕航機結構等相關領域。
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